led matrix using tb62708n

ive been reading about led matrix for a couple months now. i got 10 tb62708n off of ebay, and want to use them for a large led matrix (256) and was trying to figure out if i could. i dont under stand how if all the pins are postive pins, how do you put half to anode and half to cathode. I see that there is 4 V inputs for led voltage, can you put voltage to 2 and ground to 2 and do it that way. will the chip connect to ground, or must it be voltage. any articles or example that would point me in the right direction?


Thanks Ryan


You'd want that as a source and another IC as a sink.

I'm not sure but think an 8bit shift register should work, look at 74HC595 though it can latch it doesn't have to I think, it would take two daisy chained to get 16 which is not a big deal. http://www.nxp.com/pip/74HC_HCT595_4.html

You could also try the hef4794b, I know it can be used as a sink. http://www.nxp.com/acrobat_download/datasheets/HEF4794B_2.pdf

This has selectable outputs http://focus.ti.com/lit/ds/symlink/sn74lv8153.pdf

Beware of eating up the ram in the arduino.

so basically i can not do a matrix with just the chips i have. i need something to sink to ground correct? I assume the 595 can sink current and ground, so in that case wouldnt it be easier just to go all 595? or would it be better code wise to try and use what i have and something to sink current?

Thanks Ryan

Oh I'm sure you could do it with the chips you have it would just be harder. I suspect you could use the output of the 2nd tb62708 to drive a transistor for each LED which would provide your sink. It's just unwieldy. But I'd not give up on the tb62708, it's got great features that reduce your parts count even if you use some other IC or circuit for the sink.

As to programming it I think you can use the same data and clock lines but use separate enable/latch lines. That would save some I/O pins for other uses. I'm considering doing something like that rather than daisy chaining the HEF4794B's I am using as I want to reuse the data/clock I/O but program each chip separately.

i still do not have a full understanding on transistors. I so understand how you are saying to use them tho. what type should i use since they each one will not be passing that much current. I currently have some large mosfets, but i think they would be over kill(pulled them out of a apc). as for wiring them, ill look at something like runing a dc motor off a arduino using transistors. basically using them to switch the ground correct. im going to try and come up with something in eagle, then use batchpcb and put it together. Ill figure out the coding once i have that. Trying to do this from the ground up to learn it all, im sure there are easier ways tho.

Thanks again Ryan

This link has a general overview of the concept of an array. http://www.acm.uiuc.edu/sigarch/tutorials/ledarray/

If the IC cannot sink (provide a ground) current but can source current then it can turn a transistor on and off that can sink current. These would be turned 'on' to provide a ground for your LED. Any general purpose transistor would work, 2n2222

Here is the datasheet for the TB ic. http://www.marktechopto.com/PDFs/toshiba/ACF42D.pdf

What you're trying to do is feed an LED both a current and a ground so you can control each LED separately. You have 16 current sources with the TB chip, so you need 16 current sinks. I'm pretty sure the TB chip + transistors could provide you with that but it's 17 parts and a lot of work.

I don't have anything further. I've built one good circuit with the hef4794 that controls 16 LEDs and need to try to use the 74hc595. I'm trying to do what you're doing but right now I'm just trying to get a nice christmas ornament made.

Yeah that is what i thought. If i wanted to control 64 leds in an array, i would only need 8 2n2222, and 1 tb62708n. 8 outputs of the tb for current, 8 to the 2n2222 which then provide for sink. From what i understand of the 595 you need a bunch of resistors(one for every leg), but the tb you only need one. That being said, i think the data sheets shows that being used incorrectly on there application circuit. The show 2 tb, but only 1 has a resistor before the led source voltage. Just something i noticed. I think i have a good understanding of how to wire the array now, my biggest fear is the lack of documentation for programing using the tb62708n. I know its shiftin, so i think it will be sued close to the same as the 595? not sure about that.

Thanks Ryan

I used shiftout with the hef4794, my only complaint is it's only good for 8 bits but they will be fixing that so I an stream out as many as I need.

With the TB chip I think you'll do fine with two shiftouts if you can get the latch and enable logic right. I'd have to try one of them to see what it wants, the data sheet is lacking.

This is my code for two hef4794 chips and I'll reuse this code for the 595 chips. I'm working on a non scanning 64 led array so mine will take more chips and I might just get the TB chip as it will substantially cut down on parts but it doesn't seem to have the storage feature of the hef or 595. You'd probably not want a storage feature for a scanned array.


Good luck :)

one thing of note about the tb chip. the pin spacing is odd. about half of normal. Something that it easy to miss till you see them sitting in front of you. If you want i am willing to send a couple to you if you will help me figure these things out. I have 10, and i cant see that i will ever need over 6. 4 in an array would be massive, and 8 would just be near impossible(16384). so 10 is to much. message me if interrested.